nav {
    height: 95vh;
    width: 98.8vw;
}

.d_study {
    width: 10%;
    height: 90%;
    background-color: #3fa9f5;
    display: flex;
    align-items: center;
    justify-content: center;
    color: #ffffff;
    font-size: 7.5vh;
    text-shadow: 2px 2px 2px #333333;
}